1. Field of the Invention
This invention relates to a color image processing method and apparatus used in color image communication.
2. Description of the Related Art
Heretofore, color image communication between different kinds of apparatuses has been performed in the following manner. That is, different kinds of color image apparatuses communicate with each other through connector cables, communication network or the like for transmitting and receiving color images, such apparatuses include color scanners, color printers, and apparatuses incorporating a color scanner and a color printer. In a copying operation in an apparatus incorporating a color scanner and a color printer, such as a color copier, an input image and an output image can be compared with each other since the color scanner and the color printer are located in the vicinity of each other. Thus, it is possible to perform color correction by a black-box-like approach, that is, by a method the contents of which are unknown to the user, and to obtain a copied image which is an accurate reproduction of an original image. That is, it is easy to provide an output image having a color tone which is faithful to the color tone of an input image. On the other hand, in color image communication, since a transmitter and a receiver are in general separated from each other, it is impossible to compare a transmitted image with a received image. Accordingly, a color image is transmitted from the transmitter to the receiver without the operator knowing whether or not proper color correction has been performed.
In the above-described conventional approach, it is impossible to perform proper color correction in color image communication if the transmitting side color scanner and the receiving side color printer are not identified. Hence, the conventional approach has the following disadvantages:
(1) The receiving side cannot obtain an output image represented by accurately produced colors of an original image transmitted from the transmitting side. Hence, the hue, lightness, saturation and the like of the output image deviate from those of the original image.
(2) Even if color matching is obtained between certain kinds of apparatuses, accurate reproduction of colors is not guaranteed if the kinds of apparatus change.
A technique of selecting color correction coefficients by inputting a standard color image, and comparing an output color image obtained by processing the standard color image with the standard image has been disclosed in U.S. Pat. No. 4,888,636 and U.S. application Ser. No. 07/789,450 filed Nov. 7, 1991, both of which are commonly-assigned.
However, such a technique cannot solve the above-described problems in the transmission/reception system.
Particularly, a technique wherein errors produced in encoding and decoding processing are considered has not been proposed.